1. Field of the Invention
The present invention relates to a wire electric discharge machine provided with a disconnection repairing unit for performing disconnection repairing operation while monitoring a position of a core fixing section considering the fact that connection is disabled when the wire electrode reaches a core fixing portion while retracting in a machining route, for the purpose of performing a disconnection repairing operation for repairing disconnection of the wire electrode, when disconnection of the wire electrode occurs during machining using a function of fixing a core to a workpiece (hereinafter referred to as a core fixing function).
2. Description of the Related Art
Conventionally, there have been devised wire electric discharge machines including various core fixing functions. The core fixing function is a function for performing a core fixing, that is, a function for, by making use of an adhesion phenomenon of component particles of a wire electrode in a wire electric discharge machine to a work piece, accumulating a deposit including the component particles of the wire electrode in a machining groove of the workpiece to fix a core and the workpiece.
The core fixed to the workpiece by the deposit can be removed from the workpiece by applying an external force to the core through striking or the like. Therefore, conventional processes such as setting a residual stock removal section in a machining shape, performing electric discharge machining, and electric-discharge machining the residual stock removal section again after the end of the machining to cut off the core can be omitted. It is therefore possible to reduce a machining time and improve machining efficiency.
The core fixing function will now be explained with reference to an NC program for machining a workpiece. FIG. 8 is a program example in operating the core fixing function according to a command of the NC program. The core fixing function of the wire electric discharge machine is operated according to the command of the NC program. Note that a command code for operating the core fixing function is represented as M100. A core fixing distance is set to 2 mm.
When the program example (O0100) shown in FIG. 8 is executed, a machining result shown in FIG. 9 is obtained. FIG. 9 is a diagram showing an example of the machining result obtained when the core fixing function is operated according to the command of the NC program. Machining of a workpiece 40 is started from a machining start hole 41. A wire electrode machines a machining route 42 commanded by the program to form a machining groove 43.
When M100 is commanded in a block N104 and a block N107, the core fixing function is enabled. The machining advances while accumulating a deposit. A portion where the deposit is accumulated is referred to as a core fixing section 45. The core fixing section 45 is in a state in which the machining groove is filled with the deposit.
When the machining advances 2 mm in a state in which the core fixing function is enabled, the core fixing function is disabled. The machining advances while forming the machining groove again. The program ends in a block N111. At this point, the workpiece 40 and a core 44 are fixed by the core fixing section 45.
The core 44 can be removed by applying an external force to the core 44 by hitting the core 44 with a hammer or the like. Conventionally, as shown in FIG. 10, work for providing a residual stock removal section 51 in a machining shape, performing electric discharge machining, and electric-discharge machining the residual stock removal section 51 again in a later process to cut off the core 44 is performed. However, since the process can be omitted, it is possible to reduce a machining time and improve machining efficiency.
It is now assumed that disconnection occurs during machining performed using a core retaining function of the wire electric discharge machine. FIG. 11 is a diagram for explaining disconnection repairing performed using the core fixing function. A wire electrode is disconnected in a disconnection position 47. The wire electrode travels backward on the machining route for connection in an automatic connection position 48 (see an arrow of reference numeral 50). When the core fixing section 45 is not formed, the wire electrode travels backward from the disconnection position 47 to the automatic connection position 48 on the machining route as indicated by reference sign 50a and performs a connection operation and, moving to the disconnection position 47 along the machining route after the connection, then the machining is resumed.
As a function of automatically repairing disconnection and resuming machining when the disconnection occurs during the machining, various functions have been devised. FIGS. 12A, 12B, and 12C are diagrams showing disconnection repairing by the conventional disconnection repairing unit.
As shown in FIG. 12A, there has been devised a method of (1) returning to the machining start hole and automatically connecting the wire electrode, returning to a position where the wire electrode is disconnected on the machining route (hereinafter referred to as a disconnection position) along the machining route, and resuming the electric discharge machining from the disconnection position of the wire electrode. As shown in FIG. 12B, there has been devised a method of automatically connecting the wire electrode in an intermediate position between the disconnection position of the wire electrode and a start point of a machining block in which the disconnection of the wire electrode occurs, returning to the disconnection position along the machining route, and resuming the electric discharge machining from the disconnection position of the wire. As shown in FIG. 12C, there has been devised a method of moving to a position machined most lately among intersections of a circle having a radius drawn around the disconnection position and the machining route and automatically connecting the wire electrode, returning to the disconnection position along the machining route, and resuming the electric discharge machining from the disconnection position of the wire electrode. All the methods are methods of, after performing the automatic connection, returning to the disconnection position along the machining route and resuming the electric discharge machining from the disconnection position of the wire.
Patent Literatures disclosing techniques of the wire electric discharge machine including the core fixing function will be explained.
Japanese Patent Laid-Open No. 2012-166332 discloses a workpiece cutoff machining method of preventing a drop of a cutout object from a work piece, breaking a welding section with an external force and cutting off the cutout object without machining a residual stock removal section with electric discharge machining again, and reducing a machining time and improving machining efficiency.
Japanese Patent Laid-Open No. 2014-24132 discloses a machining program editing method of analyzing a machining program for the plate thickness of a workpiece, the number of machining members, and the specific gravity of the machining members, calculating a machining peripheral length of the machining members and an upper surface area of the shape of the machining members to calculate the mass of the machining members, and, concerning a relation between welding lengths of a retainable welding section to the workpiece of the machining members, calculating, from a map of a measurement value of a controller memory, a predetermined welding length and welding places of the retainable welding section corresponding to the mass of the machining members.
Japanese Patent Laid-Open No. 2014-14907 discloses a wire electric discharge machine and an automatic programming apparatus for the wire electric discharge machine that can optionally set places where a necessary minimum amount of a deposit is accumulated in order to fix a core to a work thin material.
Japanese Patent Laid-Open No. 2013-144335 discloses a machining program generating apparatus for a wire electric discharge machine for setting a deposit region from the shape and the weight of a core and generating a machining program on the basis of the deposit region.
Japanese Patent Laid-Open No. 2011-136409 discloses a disconnection repairing apparatus in wire electric discharge machining in which a wire electrode moves to a position machined most lately among intersections of a circle having a radius drawn around a disconnection position and a machining route and automatic connection of the wire electrode can be performed.
Japanese Patent Laid-Open No. 8-309622 discloses a disconnection repairing method of automatically connecting a wire electrode in an intermediate position between a disconnection position of the wire electrode and a start point of a block in which disconnection of the wire electrode occurs and resuming electric discharge machining.
Japanese Patent Laid-Open No. 2-145215 discloses an automatic wire supplying method of automatically connecting a wire in a disconnection position of a wire electrode or a position a small distance back from the disconnection position of the wire electrode along a machining track and resuming electric discharge machining.
Japanese Patent Laid-Open No. 56-95540 discloses a wire electric discharge machining method of, when wire disconnection occurs during machining, moving to a machining start hole, performing wire automatic supply with an apparatus for automatically supplying a wire electrode, moving to a disconnection point along an original machining track, and resuming machining from the disconnection point and a wire electric discharge machining method of stopping machining when the number of times of occurred wire disconnection is equal to or larger than the designated number of times in the same machining hole and shifting to the next machining.
In the case of the machining performed using the core fixing function as explained in the background, connection cannot be performed because the deposit is accumulated in the machining groove in the core fixing section 45 (FIG. 11, the moving route 50b to the connection position). After the wire electrode passes the core fixing section 45 and the connection is completed, if the wire electrode reaches the core fixing section 45 when returning to the disconnection position along the machining route, since the deposit is accumulated in the machining groove 43 and the machining groove 43 is buried in the core fixing section 45, the wire electrode is caught by the deposit and disconnected (FIGS. 12A, 12B, and 12C, the route 49 returning to the disconnection position). Therefore, even if the wire electrode retracts beyond a terminal of the core fixing section 45 (hereinafter referred to as a core fixing end position 46) and the automatic connection is performed in disconnection repairing, the machining cannot be resumed.
In Japanese Patent Laid-Open No. 2012-166332, when disconnection of a wire electrode occurs in a welding process, it is possible to supply the wire electrode to a machining slit at a disconnection point and continuously perform a welding process or a machining process. This relates to a core fixing function for changing an electric machining condition halfway in machining, melting a part of the wire electrode and welding a workpiece and a core, and fixing the core to the workpiece. Concerning disconnection during a core fixing function operation, connection can be performed on the site and the machining can be continuously performed. However, there is no description concerning a repairing method of disconnection that occurs after the operation of the core fixing function ends.
In Japanese Patent Laid-Open No. 2014-24132, a machining program is analyzed to automatically calculate the length and the place of a core retaining portion. Like Japanese Patent Laid-Open No. 2012-166332, concerning disconnection during a core fixing function operation, connection can be performed on the site and the machining can be continuously performed. However, there is no description concerning a repairing method of disconnection that occurs after the operation of the core fixing function ends.
In Japanese Patent Laid-Open No. 2014-14907, a core fixing place is optionally set when a core fixing function is used. However, there is no description concerning a repairing method of disconnection that occurs after the operation of the core fixing function ends.
Japanese Patent Laid-Open No. 2013-144335 discloses a machining program generating apparatus for a wire electric discharge machine that can deposit components of a wire electrode on a core not via complicated work. However, there is no description concerning a repairing method of disconnection that occurs after the operation of the core fixing function ends.
In Japanese Patent Laid-Open No. 2011-136409, automatic connection is performed in a position on a machining route a certain distance apart from a disconnection position to reduce time for returning to the disconnection position from a connection position, eliminate disorder of a machining liquid flow, and improve a connection ratio. However, if a core fixing portion is present between the connection position and the disconnection position, disconnection occurs again in the return to the disconnection position.
In Japanese Patent Laid-Open No. 8-309622, automatic connection is performed in a machining groove in an intermediate position between a disconnection position and a start point of a block in which disconnection occurs and time until electric discharge machining resumption after the disconnection is reduced. However, like Japanese Patent Laid-Open No. 2011-136409, if the core fixing portion is present between the connection position and the disconnection position, disconnection occurs again in the return to the disconnection position.
In Japanese Patent Laid-Open No. 2-145215, when connection in a disconnection position is impossible, machining cannot be resumed by a method disclosed in the patent literature. The patent literature is different from this application for performing the automatic connection between the disconnection position and the core fixing section.
In Japanese Patent Laid-Open No. 56-95540, automatic connection is performed in a machining start hole. However, like Japanese Patent Laid-Open No. 2011-136409 and Japanese Patent Laid-Open No. 8-309622, if the core fixing section is present between the machining start hole and the disconnection position, disconnection occurs again in the return to the disconnection position. A condition for shifting to the next machining is that the number of times of disconnection of the wire is equal to or larger than the designated number of times. Therefore, the patent literature is different from the present invention, which checks presence or absence of the core fixing section and determines whether to make a shift to the next machining.